Multifunctional nanoheater based on NaGdF_4:Yb^3+, Er^3+ upconversion nanoparticles

Abstract

Upconversion nanoparticles (UCNPs) provide an ideal platform for achieving multifunction, such as multimodal imaging, sensing, therapy, etc., mainly by combining with other nanomaterials to construct complicated heterogeneous nanostructures. Multifunctional integration on a simple single-phase structure still is an open question and poses a big challenge. Here we show that small-sized NaGdF(4):Yb(3), Er(3+) UCNPs (~7.5 nm) can simultaneously possess upconversion luminescence (UCL), temperature sensing, paramagnetic and photothermal conversion properties, endowing them great potential for photothermal treatments with real-time imaging and temperature monitoring. Effects of Yb(3+) concentrations, nanoparticle sizes and core/shell structures on the light-to-heat conversion capability of UCNPs were also investigated, and the results were discussed on the basis of the variation in absorption rates and non-radiative relaxation probabilities of UCNPs. There is a competition between UCL and light-to-heat conversion processes. Higher UCL efficiency and enhanced photothermal conversion properties can be realized on UCNPs with the active-core/active-shell structure due to enhanced absorption rates.

Photoresponsive Biomimetic Protocells for Near-Infrared-Light-Regulated Phototheranostics

“…Both UCNPs and BPQDs solutions rose < 10°C within 30 min under the corresponding laser excitation, consistent with several literature reports. 36,55,56 Therefore, our above results confirmed that the thermal effect in the UBAL protocells has three origins: the first is from the UCNPs solution, the second is from BPQDs absorbing the converted visible light to generate extra heat, and the third is from BPQDs excited by an 808 nm laser. Furthermore, the thermal effect of UBAL was derived primarily from the heat absorption of BPQDs.…”

Electrochromic Switch Devices Mixing Small‐ and Large‐Sized Upconverting Nanocrystals

“…The thermal effect on the emission intensity cannot be ascribed to eventual particle coalescence or to a modification of the surface induced by thermal damage of the capping ligands since both effects would produce irreversible changes in the UCNPs' emission profiles. Although the thermal emission quenching effects of large nanocrystals and bulk upconverting materials are well known, only recently the anomalous behavior of small‐sized UCNPs was demonstrated in a set of systematic studies performed by Jiang and co‐workers . Initially, these authors suggested that the phonon density of states is modified by quantum confinement reducing the number of available low‐energy modes.…”

“…Although several hypotheses have been formulated to explain this intriguing thermal effect, the matter remains an open question . Systematic studies on UCNP emission intensity controlled by a thermal field have already been performed by Li et al and Shao et al These authors showed that the emission intensity is enhanced with the increase of temperature for UCNPs smaller than a critical size of 20–30 nm, whereas emission quenching occurs for larger particles. These effects were used to control the nanoparticles' emission color via modulation of the irradiation laser power, which obviously affected the total intensity of the emissions, or by directly varying the temperature through complex heating systems, involving a copper sample cell and a ceramic plate controlled by a proportional‐integral‐derivative (PID) regulator .…”

Lanthanide‐Based Thermometers: At the Cutting‐Edge of Luminescence Thermometry

“…Furthermore, since 2015, it was understood that the thermal effects on the light emission of organic‐capped UCNPs is a size‐dependent phenomenon. Systematic studies on the emission intensity of the particles upon distinct temperatures were performed by Li et al and Shao et al The authors showed that at higher temperatures (e.g., 300–500 K) whereas the emission intensity is enhanced for particles smaller than a critical size (e.g., 20–30 nm), it is quenched for bigger particles. This effect was used to control of NPs' emission color via modulation of the irradiation laser power or directly varying the temperature (through complex heating systems) .…”